NAME
swapctl
—
modify swap configuration
LIBRARY
library “libc”
SYNOPSIS
#include
<unistd.h>
#include <sys/swap.h>
int
swapctl
(int
cmd, void *arg,
int misc);
DESCRIPTION
Theswapctl
function is used to add and delete swap
devices, and modify their configuration.
The cmd parameter specifies the operation to be performed. The arg and misc parameters have different meanings, depending on the cmd parameter.
- If cmd is
SWAP_NSWAP
, the current number of swap devices in the system is returned. The arg and misc parameters are ignored. - If cmd is
SWAP_STATS
, the current statistics for swap devices are returned in the arg parameter. No more than misc swap devices are returned. The arg parameter should point to an array of at least misc struct swapent structures:struct swapent { dev_t se_dev; /* device id */ int se_flags; /* entry flags */ int se_nblks; /* total blocks */ int se_inuse; /* blocks in use */ int se_priority; /* priority */ char se_path[PATH_MAX+1]; /* path to entry */ };
The flags are defined as
SWF_INUSE in use: we have swapped here SWF_ENABLE enabled: we can swap here SWF_BUSY busy: I/O happening here SWF_FAKE fake: still being built
- If cmd is
SWAP_ON
, the arg parameter is used as a pathname of a file to enable swapping to. The misc parameter is used to set the priority of this swap device. - If cmd is
SWAP_OFF
, the arg parameter is used as the pathname of a file to disable swapping from. The misc parameter is ignored. - If cmd is
SWAP_CTL
, the arg and misc parameters have the same function as for theSWAP_ON
case, except that they change the priority of a currently enabled swap device. - If cmd is
SWAP_DUMPDEV
, the arg parameter is used as the pathname of a device to use as the dump device, should the system panic. - If cmd is
SWAP_GETDUMPDEV
, the arg parameter points to a dev_t, which is filled in by the current dump device.
When swapping is enabled on a block device, the first portion of
the disk is left unused to prevent any disklabel present from being
overwritten. This space is allocated from the swap device when the
SWAP_ON
command is used.
The priority of a swap device can be used to fill faster swap devices before slower ones. A priority of 0 is the highest, with larger numbers having lower priority. For a fuller discussion on swap priority, see the SWAP PRIORITY section in swapctl(8).
RETURN VALUES
If the cmd parameter is
SWAP_NSWAP
or SWAP_STATS
,
swapctl
() returns the number of swap devices, if
successful. The SWAP_NSWAP
command is always
successful. Otherwise it returns 0 on success and -1 on failure, setting the
global variable errno to indicate the error.
ERRORS
swapctl
() succeeds unless:
- [
EACCES
] - Search permission is denied for a component of the path prefix.
- [
EBUSY
] - The device specified by arg has already been made available for swapping.
- [
EFAULT
] - arg points outside the process' allocated address space.
- [
EINVAL
] - The device configured by arg has no associated size, or the cmd was unknown.
- [
EIO
] - An I/O error occurred while opening the swap device.
- [
ELOOP
] - Too many symbolic links were encountered in translating the pathname.
- [
ENAMETOOLONG
] - A component of a pathname exceeded {
NAME_MAX
} characters, or an entire path name exceeded {PATH_MAX
} characters. - [
ENOENT
] - The named device does not exist. For the
SWAP_CTL
command, the named device is not currently enabled for swapping. - [
ENOTDIR
] - A component of the path prefix is not a directory.
- [
ENXIO
] - The major device number of arg is out of range (this indicates no device driver exists for the associated hardware); or the block device specified by arg is not marked as a swap partition in the disklabel.
- [
EPERM
] - The caller is not the super-user.
SEE ALSO
HISTORY
The swapctl
() function call appeared in
NetBSD 1.3. The se_path member
was added to struct swapent in NetBSD
1.4, when the header file was also moved from
<vm/vm_swap.h>
to its
current location in
<sys/swap.h>
.
AUTHORS
The current swap system was designed and implemented by Matthew Green <mrg@eterna.com.au>, with help from Paul Kranenburg <pk@NetBSD.org> and Leo Weppelman <leo@NetBSD.org>, and insights from Jason R. Thorpe <thorpej@NetBSD.org>.